In a liquid effluent free bleached pulp mill, in which bleached pulp is formed by digesting cellulosic fibrous material and bleaching and purifying the pulp and in which spent pulping liquors are subjected to recovery and regeneration to form fresh pulping liquor, liquid effluents from the bleaching and purification operations (bleach plant effluent) are discharged into the recovery and regeneration operation.
The organic materials content of the bleach plant effluent is burned off in the recovery furnace of the recovery and regeneration operation and the aqueous phase is evaporated in the recovery and regeneration operation.
Owing to the high cost of evaporating water in a pulp mill, in the interests of minimizing operating costs, it is desirable to decrease the total volume of bleach plant effluent which must be discharged into the pulp mill recovery and regeneration operation and hence minimize the total evaporation load. It is also desirable that any bleach plant effluent volume decrease not significantly adversely affect the pulp quality obtained.